제출 #791557

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
791557		ttamx	Star Trek (CEOI20_startrek)	C++14	7 / 100	13 ms	2728 KiB

startrek

#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

const int N=1e5+5;
const ll mod=1e9+7;

ll binpow(ll a,ll b){
    ll res=1;
    while(b>0){
        if(b&1)res*=a,res%=mod;
        a*=a,a%=mod;
        b>>=1;
    }
    return res;
}

int n;
ll d,ans,sum;
vector<int> adj[N];
ll dp[N][2];
bool dp1[N],dp2[N];

void dfs(int u,int p){
    for(auto v:adj[u]){
        if(v==p)continue;
        dfs(v,u);
        dp1[u]|=!dp1[v];
    }
}

void dfs2(int u,int p,bool w){
    int cnt=!w;
    dp2[u]=dp1[u]|!w;
    for(auto v:adj[u]){
        if(v==p)continue;
        cnt+=!dp1[v];
    }
    for(auto v:adj[u]){
        if(v==p)continue;
        dfs2(v,u,cnt-!dp2[v]>0);
    }
}

bool dfs3(int u,int p,int t,bool w){
    bool res=true;
    for(auto v:adj[u]){
        if(v==p)continue;
        res&=dfs3(v,u,t,w);
    }
    if(u==t)res&=w;
    res^=true;
    return res;
}

int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    cin >> n >> d;
    if(n==2)cout << binpow(4,d),exit(0);
    for(int i=1;i<n;i++){
        int u,v;
        cin >> u >> v;
        adj[u].emplace_back(v);
        adj[v].emplace_back(u);
    }
    dfs(1,1);
    dfs2(1,1,true);
    for(int i=1;i<=n;i++)sum+=dp2[i];
    for(int i=1;i<=n;i++)ans+=sum*dfs3(1,1,i,true)+(n-sum)*dfs3(1,1,i,false);
    cout << ans;
}

• Subtask 1: 0 / 0
• Subtask 2: 7 / 7
• Subtask 3: 0 / 8
• Subtask 4: 0 / 15
• Subtask 5: 0 / 15
• Subtask 6: 0 / 20
• Subtask 7: 0 / 20
• Subtask 8: 0 / 15